Hepatitis B virus (HBV) infection is a public health problem of worldwide importance. HBV causes an in-curable and sometimes fatal liver disease which strikes an estimated 20,000 new victims every year in the United States alone. In the Far-East, Africa and Eastern Europe about 10% of the population are chronic carriers of HBV with the result that chronic active hepatitis and liver cirrhosis are major causes of mortality. Further, there is strong evidence that carriers of HBV are far more susceptible to liver cancer, HBV being one of the few viruses known to be involved in human cancer.
Thus, there exists an urgent need for the production of a safe and economically feasible vaccine for protection against HBV infection. Several approaches have been taken to produce such a vaccine. (See Tiollais et al., Nature 317: 489-495 (1985); Patzer et al., Vaccines 85: 261-264, Cold Spring Harbour (1985); and Zuckerman, Infection 13: 61-71, Supplement A (1986) for reviews.)
As described in the above reviews, the basic component of all the vaccines that have been produced is the Hepatitis B surface antigen (HBsAg). It was originally isolated from the plasma of chronic sufferers of HBV infection and employed as an effective vaccine against HBV infection.
HBsAg in the plasma of HBV-infected carriers is present both in the 42 nm HBV infectious viral particles (Dane Particles) and in the form of a non-infectious 22 nm particle which is free of HBV-DNA and other HBV structural proteins. These 22 nm particles are overproduced in both HBV chronic human carriers or during HBV viremia. These 22 nm particles are secreted by HBV transformed hepatoma cell lines.
The 22 nm HBsAg particles, which are highly immunogenic are composed of six related proteins: (a) the major proteins P-24, non-glycosylated form of molecular weight 24,000 daltons (24K) and GP-27, the glycosylated form of P-24, of molecular weight 27,000 daltons (27K). These are encoded by the S region of the HBV genome, and have 226 amino acids; (b) the minor proteins GP-33, a single glycosylated form of molecular weight 33,000 daltons (33K) and GP-36, a double glycosylated form of molecular weight 36,000 daltons (36K). These are encoded by the Pre-S2 and S region of the HBV genome and have 281 amino acids (226 S region +55 Pre-S2 region); (c) the minor proteins P-39, a non-glycosylated form and GP-42, a glycosylated form of P-39 having respective molecular weights of 39,000 and 42,000 daltons (39K, 42K). These are encoded by the Pre-S1, Pre-S2 and S region of the HBV genome and have between 389 and 400 amino acids (226 S +55 Pre-S2 +[108-119]Pre-S1). Thus, all the proteins of the HBsAg 22 nm particles are encoded in the same uninterrupted sequence of HBV genome DNA, their final form depending on where gene expression (transcription and translation) was initiated and whether and to what extent they were glycosylated post-translationally.
22 nm HBsAg particles can be assembled from P-24/GP-27 (S region) independently of Pre-S2 and Pre-S1 products. Recently, it has been shown that the Pre-S2 specific proteins, GP-33 and GP-36, and the Pre-S1 specific proteins, GP-39 and GP-42, have antigenic determinants independent of P-24 and result in an enhanced immunogenicity when present in HBsAg 22 nm particles.
Further, when the Pre-S2 and Pre-S1 proteins are present the 22 nm HBsAg particles have the ability to bind polymerized human serum albumin which is directly related to the ability of HBV viral particles being able to bind target cells during HBV infection. Thus, HBsAg particles containing both the Pre-S and the S region protein determinants can be employed as a vaccine that will elicit a response to neutralize viral particles and to prevent such particles from infecting target cells. In this way, such a vaccine offers effective long term protection against HBV infection (for example, see Persing et al., Proc. Natl. Acad. Sci. USA 82: 3440-3444 (1985); Neurath et al., Nature 315: 154-156 (1985); Neurath et al., Cell 46: 429-436 (1986); petit et al., Mol. Immunol. 23: 511-523 (1986); and Milich et al., J. Immunol. 137: 315-322 (1986).